ovl: Fix info leak in ovl_lookup_temp()
The function uses the memory address of a struct dentry as unique id.
While the address-based directory entry is only visible to root it is IMHO
still worth fixing since the temporary name does not have to be a kernel
address. It can be any unique number. Replace it by an atomic integer
which is allowed to wrap around.
Signed-off-by: Richard Weinberger <richard@nod.at>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Cc: <stable@vger.kernel.org> # v3.18+
Fixes: e9be9d5e76e3 ("overlay filesystem")
diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
index 1560fdc..74e6964 100644
--- a/fs/overlayfs/dir.c
+++ b/fs/overlayfs/dir.c
@@ -14,6 +14,7 @@
#include <linux/cred.h>
#include <linux/posix_acl.h>
#include <linux/posix_acl_xattr.h>
+#include <linux/atomic.h>
#include "overlayfs.h"
void ovl_cleanup(struct inode *wdir, struct dentry *wdentry)
@@ -37,8 +38,10 @@
{
struct dentry *temp;
char name[20];
+ static atomic_t temp_id = ATOMIC_INIT(0);
- snprintf(name, sizeof(name), "#%lx", (unsigned long) dentry);
+ /* counter is allowed to wrap, since temp dentries are ephemeral */
+ snprintf(name, sizeof(name), "#%x", atomic_inc_return(&temp_id));
temp = lookup_one_len(name, workdir, strlen(name));
if (!IS_ERR(temp) && temp->d_inode) {